Typhoid Mary

Perhaps the strangest story in the history of epidemics: an outbreak traced to a single person — and stopped by quarantining her.

Mary Mallon was born in Ireland in 1869 and immigrated to the United States as a teenager. She found work as a cook in affluent households in and around New York City.

Mary was an asymptomatic carrier of typhoid bacteria and never fell ill herself. Long Island — where the rich lived, far from the muck and mire of the city — seemed safe from typhoid. Then one by one, the families Mary cooked for began falling sick.

It was wealthy banker Charles Henry Warren whose family's illness set the investigation in motion. Typhoid was a disease of the poor; it was not supposed to strike the wealthy. A sanitary engineer and typhoid researcher named George Soper was hired to find the source. He interviewed everyone in the Warren household and found nothing — until he learned of the family's temporary cook on their summer vacation. She had cooked for them about three weeks earlier — and typhoid's incubation period can stretch for weeks.

Tracking Mary down was difficult. Soper eventually found her working in another wealthy household and told her he believed she was spreading the disease. Mary was furious. She had never been sick in her life — how could she be the carrier? She threw him out of her kitchen. But when that household also fell ill, Soper knew he was right. He traced her employment through the preceding years and found typhoid outbreaks following her from home to home. Soper directly attributed 51 cases of typhoid — and three deaths — to Mary.

Public health officials isolated Mary on North Brother Island, in New York's East River. She was released in 1910 on the condition that she never work as a cook again — and took work at a laundry, which paid far less. Convinced she was no danger, she changed her name and went back to cooking under aliases, in houses, hotels, and restaurants — leaving more outbreaks behind her before she vanished each time.

Finally, Soper tracked her down again. In 1915 she was returned to forced quarantine on North Brother Island, where she remained for 23 years until her death in 1938. In 1909, William Randolph Hearst's New York American had christened her "Typhoid Mary" — making her famous nationwide.

Typhoid is caused by the bacterium Salmonella typhi, spread through contaminated food and water via the fecal-oral route, and today is treated with antibiotics. In Mary's time there was no cure — and no way for an asymptomatic carrier to know she was infecting others.

Originally published April 2020.